Question : The average of $n$ observations is 40. If one observation of value 80 is added, then the average of all the observations is 41. What is the value of $n$?
Option 1: 40
Option 2: 39
Option 3: 38
Option 4: 43
Correct Answer: 39
Solution : Given: The average of $n$ observations is 40. One observation of value 80 is added, and then the average of all the observations is 41. The initial number of observations = $\frac{\text{(The new observation – The new average)}}{\text{The change in average}}$ ⇒ $n=\frac{80–41}{1}$ ⇒ $n=39$ Hence, the correct answer is 39.
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